This invention relates to synchro-mesh type gear transmissions of the type used in motor vehicles, and more particularly, to a gear transmission provided with means for the reduction of gear backlash noise.
In engines for motor vehicles, the speed of engine rotation and the corresponding output torque vary over a large range. Gear-type power transmissions which are generally used with such engines produce annoying gear backlash noise which cannot be ignored. The gear backlash noise is not very significant when the engine is running at high speed, because during such operation the rotation speed and torque vary over a relatively small range, while air intake suction noises, and exhaust noises, are louder than when the engine is rotating at low speed. However, when the vehicle is stopped and the engine is idling, even small variations in the actual speed of rotation of the engine are relatively larger than when the engine is operating at high speed. During such low speed operation, large relative speed differentials may occur between an input gear and a counter input gear which is in direct engagement with the input gear, thereby producing relatively loud gear backlash noise.
The magnitude of gear backlash noise is related to frictional resistance, which is affected by the viscosity of the lubrication oil. For example, as the temperature of the lubrication oil increases, and the frictional resistance between transmission components decreases below a certain value, gear backlash noise is generated.
An improved synchro-mesh type gear transmission which reduces gear backlash noise has been proposed in Japanese Utility Model Publication No. 53-6755. The transmission described therein is provided with a clutch hub having axial slots in which springs are inserted. The springs urge a synchronizer ring against a conically tapered surface of a shift gear, thereby exerting a frictional resistance against the movement of the shift gear. However, in this known gear transmission, no means are provided for guiding the springs, thereby allowing the springs to be disadvantageously deformed in the direction in which the synchronizer ring rotates.
It is, therefore, an object of the present invention to provide a new and improved synchro-mesh type gear transmission which eliminates the possibility of undesired spring deformation.
It is another object of the present invention to provide a new and improved synchro-mesh type gear transmission which includes spring means for exerting a frictional resistance by urging a synchronizer ring against a driven shift gear, in such a manner that gear backlash noise is eliminated while the spring means are prevented from being undesirably deformed.